This is a double-blind, randomized, placebo-controlled, multicenter study to assess the safety and efficacy of orally administered SP-303 for the treatment of diarrhea in persons with AIDS. Participatants will undergo screening including blood test, be hospitalized in the GCRC for 7 days to have stool collections done daily, recieve study medication and have follow up visits on days 14, 21,28, and 35.